LONDON, UK -- Tesco, the UK's largest supermarket group, has admitted that their 'value burgers' may contain up to 29% horse meat, despite the wrapper stating 'beef'.

Irish scientists said they had discovered that the meat was contaminated two months ago. However, they did not act because they might have had to explain why they were testing UK products instead of those from Irish stores. The news eventually leaked after an excess of Guinness at the Irish scientists' 'after work drinks,' which started on Friday and continued through the weekend 'because of the snow.'

The Food Standards Agency was criticised yesterday after admitting it had never carried out tests for horse meat on food sold in Britain, because they didn't know that horse meat was on sale. Tim Lang, a professor of food policy at City University, London, said: 'It could have been going on for years but we wouldn’t know about it because we have never conducted tests.'

Under European regulations, it is an offence for retailers to mis-label food, but Tesco were quick to claim the horse meat was a 'free gift' with every pack, and therefore was exempt.

The scandal - dubbed 'riding-gate'. by the tabloid press, has led to a certain level of confusion among Tesco customers, interviewed outide a store in Chipping Sodbury:

“I went to a Tesco café yesterday and ordered a burger. They asked me if I wanted anything on it, and I said: ‘Yes — a fiver each way.”

~ Barry Gardiner, Labour MP and satisfied diner

“My mum told me I should watch what I eat. So, I'm going to the Grand National next year.”

~ Jim, Overweight teenager

“My daughter asked me for a pony for her birthday, so I'm going to buy her a Tesco Quarter Pounder.”

~ Selwyn Gummer, proud father

Tesco added to the damage by tweeting, 'We're off to hit the hay' after an evening fending off horse meat jokes.

A spokesperson stated this morning, 'There is no truth in the rumour that any of our products contain zebra meat - the pattern of stripes is a bar code, not a serving suggestion.'

Tesco's rival supermarkets - ASDA, Sainsbury's and Morrison - are believed to be researching product lines to compete with Tesco, suggestions including albatross, unicorn on the cob and cat-fish fillets. A mystery shopper asking for 'quarter pandas' was asked to leave a store in Scunthorpe this morning.

Sources discount rumours that Tesco may keep ahead of rivals by introducing Rook Tokens or Gift Vultures; the Tesco Clubcard is seen as a marketing success, except by baby seals.